Safety control apparatus for fuel burners



g- 1943- c K. STROBEL ET AL 2,448,475

SAFETY CONTROL APPARATUS FOR FUEL BURNERS Filed Oct. 27', 1942 INVENTOR. CHARLES K. \STRQBEL. B STANLEY L/IKOTA.

ATTORNE).

Patented Aug. 31, 1948 .1 2,448,475 sm'rr con'rnor. msna'rus roa FUELBUBNE Charles K. Strobel and Stanley J. Lakota, Pittsburgh, Pa aulgnors to Robertshaw-Fulton Control: Company, a' corporation of Delaware Application October 27, 1942, Serial No. 463,492

17 Claims. (01. 158-1171) This invention relates to safety control apparatus for fuel burners and, more particularly, to electrically operated controls therefor.

Safety control apparatus of the kind described may include electric ignition means, such as a coil, which is energized during the starting period and deenergized during the normal running period of the burner. When the safety control operates to shut off the flow of fuel to the burner, as may occur upon undesired extinguishment of the burner flame, the apparatus remains inoperative until the failure to operate is noticed. In consequence, although no danger from escaping fuel is present, the cessation of normal operation may extend over a considerable period of time and cause trouble and loss due to the prolonged lack of the burner heat for some required purpose.

An object of this invention is to deenergize the burner igniting means during normal running conditions and promptly reenergize the. same whenever the safety control has operated.

Another object of the invention is to delay the reenergizing of the igniter sufficiently to permit the escape of unburned fuel remaining from a previous operation.

Another object of the invention is to reduce the shut-01f time to a minimum upon the occurrence of dangerous conditions, such as undesired extinguishment oi the burner flame.

Another object of the invention is to permit operation of the burner, if desired, in the event of failure of the igniting means.

Other objects and advantages will become apparent from the following description taken in connection with the accompanying drawing, which is a schematic view of a safety control apparatus for a gaseous fuel burner embodying this invention.

Referring more in detail to the drawing, a gaseous fuel burner I0 is supplied with fuel from a main fuel pipe i2. The fuel supply is controlled by a main valve it which, in this instance, is adapted for manual operation but which may be arranged for thermostatic operation if desired. Preferably, a main switch for the electric circuit to be described is included in the main valve I4 and is arranged to establish the circuit whenever the valve is opened. Interposed in the fuel supply pipe I 2 between the main valve I4 and the burner i0 is an electromagnetic gas valve it of any suitable type which may be arranged, as in this instance, to be opened by energization of the electromagnet and closed by gravity upon deenergization thereof.

receive fuel from the pipe I2 when the main valve is opened, The pilot burner is adapted to be ignited by an electric igniting means 22, such as an ignition coil, and, in turn, will ignite the fuel issuing from the main burner II! when in operation. Electrical energy for the operation of the electromagnetic valve l6 and the igniting means 22 is supplied through line wires 24 -28 connected to the primary or a transformer 28.

The electric circuit to the electromagnetic valve I8 and ignition means 22 is controlled by a control relay 30. This relay 30 includes a hinged armature 32 carrying a core 33 and adapted to return to a normal position by gravity, springs or other means (not shown). In this normal position of the armature 32, that is, when the operating means is dee'nergized, engagement is made thereby with a fixed contact 34 to complete a circuit through the electromagnetic valve It. The armature 32 carries, on the side opposite that engaging contact 34, a movable contact 38 which is insulated therefrom and is adapted to engage a fixed contact 38 to complete a circuit through the igniting means 22 when the armature moves from its normal to its attracted position. In this attracted position of the armature engagement is also had thereby with a fixed contact 40 which is located on the same side as contact 38 to establish a shunt around the electromagnetic valve IS.

A heat responsive or flame sensitive element 42 is positionedto be exposed to the flame of the pilot burner is for causing operation of the relay 30 to remove the aforementioned shunt for the electromagnetic valve i6 and simultaneously to deenergize the ignition means 22. The flame sensitive element 42 may take the form of a coil of wire of material having a normally relatively low resistance. and a positive temperature coefllcient of'resistance. Such devices, commonly termed ballast resistors," are thermally responsive to the passage of current therethrough but in this embodiment the element 42, hereinafter termed the ballast resistor, is primarily responsive to the'heat of the pilot burner flame. Accordingly,. it will be understood that it is the variatio'nin resistance in response to the pilot burner which renders the ballast resistor useful in this invention.

As'indicated in the drawing, the main burner l0, pilot burner 18, ignition means 22 and ballast resistor 42 are adapted to be mounted in the chamberll'of an oven or like device. In such arrangements, unburned fuel may be present in A pilot burner II is supplied with fuel from a the vicinity of the main burner l0 following the circuit upon an overcurrent.

' The apparatus is shown in the normal run-' closure of. the electromagnetic valve l6 and such fuel sho d be permitted to flow away before the ignition eansis energized to ignite the pilot burner. To this end, a purge period is provided in the sequence of operation of the control by a thermally operated switch 46 which maintains a shunt around the ignition means 22 for a predetermined period following closure of the electromagnetic valve l6. The switch 46 comprises a bimetal element 48 carrying a contact 68 which is therefore movable and adapted to engage a fixed contact 62 when the bimetal element 48 is sufllciently heated.

A resistor 64 is placed in circuit with the ignition means 22 by operation of the relay 38 to close contacts 36 and 38 and serves to regulate the current to the ignition means and also to permit the shunting thereof by the bimetal switch 46. A second resistor 66 is placed in circuit with the ballast resistor 42 "by operation .of the relay 38 to disengage armature 32 from contact 34 and serves to shorten the pick-up and release times of the relay.

A cut-out 68 is incorporated in the circuit of the ballast resistor 42 to protect against the continued escape of unburned gas, which might be caused by a defect in the relay, preventing pickup of the armature and subsequent closure of the magnetic gas valve, when the circuit is energized and the ballast resistor 42 is not heated by the flame of the pilot burner I8. The large steady current through the ballast resistor 42 which in such event would remain cold will cause the cut-out to operate although a large inrush current will notcause it to open the circuit. Hence, the cut-out 58 is preferably of the thermal type provided with time-lag operation having predetermined time-current characteristics and usually containing a heater element in addition to and afiecting a fusible member which opens ning position .of the main burner 18 in which the electromagnetic valve I6 is energized and the ignition means 22 deenergized. At the start of operation to obtain this running position, the control relay 38 occupies the normal position shown and the contacts 58 and 52 of the bimetal switch 46 are open due to the bimetal arm 48 being unheated. Opening of the main valve l4 permits fuel to flow to the pilot burner l8 and also in the main fuel pipe i 2 as far as the electromagnetic valve l6. which is normally closed. Due to operation of the main switch as described when valve I4 is opened a circuit is then esta-blished as follows: From the secondary of the transformer 28 to wire 68, main switch of valve I4, wire 62, wire 64, coil 66 of control relay 38, wire 68, electromagnetic valve 16, wire 18, heater coil "I2 of bimetal switch 46, wire 14, armature 32 of control relay 38, contact 34, wire 16, wire 18, ballast resistor 42, wire 88, cut-out'58 and, wire 82 back to the secondary of. the transformer 28. Energization of the operating means of the control relay 38 will attract the armature 32 causing it to move into engagement with contact 48 and also causing engagement of contacts-36 and 38 to establish two parallel circuits connected across the points designated A and B. At the instant the main switch of valve i4 .closes, the electromagnetic valve is energized and will admit fuel to the main fuel pipe l2 to the main burner l8. Such operation of the main electromagnetic valve I6 is momentarmhowever', and immediate deenergizing thereof occurs due circuit the electromagnetic valve 16 and the bimetal switch 46 are both shunted.

In the other parallel circuit established by operation of the control relay 88 the current flows from B, wire 86; contacts 36 and 38, wire 88, resistor 64, wire 98, ignition means 22, wire 82 and wire 82 back to point A. Energlzation of the ignition means 22 will ignite the fuel flowing from the pilot burner causing the ballast resistor 42 to become heated in response thereto.

The increase in resistance of the ballast resistor 42, due principally to the heat of the pilot. burner, reduces the current through the operating means of control relay 38 suillciently to cause the armature 32 to resume its normal position. The circuit then established is as described at the instant of turning on of themain switch of valve l4. In this position of armature 32 the electromagnetic valve I6 is energized and actuated to open position permitting fuel to flow to the main burner I8 while the ignition means with fixed contact 62.. A shunt is then established around the ignition means 22 by way of wire 94 connecwd at one end to contact 62 and to wire 88 at the other end and by wire 86 connected' at one end to contact 68 and to wire 82 at the other end.

Should the main and pilot burners become extinguished without operation of the main valve I 4 theballast resistor 42 immediately starts to cool ofl and its resistance becomes correspondingly decreased. Consequently, through the operating means of control relay 38 becomes large enough to attract the armature 32 thereof to move it out of engagement with contact 34 and into engagement with contact 48 thus also closing contacts 36 and 38. A shunt is then established around the electromagnetic valve l6 and bimetal switch 46 and the current supply at the points A and B is connected to the circuit of the ignition means 22 as previously described. Due, however, to the shunt established around the ignition means 22 by the bi-. metal switch 46, the ignition means remains effectually deenergized. It is apparent that the cooling period is longer than that of the ballast resistor 42 so as to allow a suitable period between the time of closing of the electromagnetic valve [6 and complete reenergizing of the ig nition means 22 by operation of the bimetal switch 46 to permit any unburned fuel from the a main burner! to flow away. When the contacts 58 and 62- of the bimetal switch are opened due to cooling of the bimetal 48, the ignition means 22 becomes completely energized and the sequence of operation proceeds as previously described.

' The purpose of the resistor 66 in shortening the pick-up and release time of the control relay 38 is accomplished, as will be clear by the foregoing description. Thus, when a relatively large the current current is needed for movement of the armature 32 out of engagement with contact I, the resistor 58 is shunted. Then, after the pick-up has been accomplished, the resistor 56 is introduced into the circuit so as to drop the relay current to a value immediately above that at which the relay operating means will fail to hold the armature 32.

These safety features include provision for cutting off the supply of fuel to the main burner III in the event that the ballast resistor 42 becomes open-circuited. It will be apparent that in such event the electromagnetic valve IS in circuit therewith will Moreover, if the ignition means 22 should fail the apparatus may still be operated by lighting the pilot burner l8 with a match, although in such usage the apparatus would not recycle.

While a preferred embodiment of the invention has been shown and described, it is apparent that many modifications will occur to those skilled in the art. Hence, the invention is not to be deemed limited to the form shown and described or otherwise than as included in the scope of the claims appended hereto.

We claim: v

1. A safety control for fuel burners having main and pilot burners, comprising a source of current supply, means movable between positions for controlling the supply of fuel to the main burner, a control device adapted to receive current from said source and being thereby operable for causing movement of said means between said positions, means responsive to one operation of said device for igniting the pilot burner, and means responsive to a flame at the pilot burner for reducing said current to said device and there: by causing another operation of said device to change the position of said movable means and render said igniting means inoperative,

2. A safety control for fuel burners having main and pilot burners, comprising a source of current supply, means movable between open and closed positions for controlling the supply of fuel to the main burner and being biased to said closed position, a control device in circuit with said means adapted to receive current from said source and being thereby operable for causing movement of said means under said bias to closed position preventing supply of fuel to th main burner, means responsive to said operation of said device for igniting the pilot burner, and means responsive to a flame at the pilot burner for reducing said current to said device and thereby causing another operation of said device to reverse the position of said movable means a t said bias and simultaneously render said igniting means inoperative.

3. A safety control for fuel burners having main and pilot burners, comprising a source of current supply, electrically operable means movable between. positions for controlling the supply of fuel to the main burner, a control relay adapted to receive current iromsaid source and being thereby operable for causing movement of said means between said positions, an electric igniter energized by said operation of said relay and adapted to produce a flame at the pilot burner, and a thermal resistance element adapted to vary the current supply to said relay in response to the pilot burner flameand thereby cause another operation of said relay to change the position of said movable means and deenergize the igniter.

4. A safety control for fuel burners having main and pilot burners, comprising electrically immediately be deenergized.

operable means movable between positions for controlling the supply of fuel to the main burner.

an energizing circuit for said movable means, a a control relay in said circuit having a pair of normally open and a pair of normally closed contacts, said movable means being energized for movement between said positions by operation of said relay to reverse the said normal position of said pairs of contacts, an electric igniter adapted when energized to produce a flame at the pilot burner, an energizing circuit for said igniter includin said pair of normally open contacts, and means responsive to a flame at the pilot burner for causing operation of said relay to restore said normal position of said contact pairs thereby to change the position of said movable means and open the circuit of said igniter.

5. A safety control for fuel burners having main and pilot burners, comprising electrically operable means movable between open and closed positions for controlling the supply of fuel to the main burner, an energizing circuit for said movable means, a control relay in said circuit having a pair of normally open and a pair of normally closed contacts, said movable means being energized for movement to open position in the said normal position of said contact pairs and deenergized by operation of said relay to reverse the said normal position of said contact pairs, an electric igniter adapted when energized to produce a flame at the pilot burner, an energizing circuit for said igniter including said pair of normally open contacts, a main switch for closing the circuit of said movable means and causing said relay operation to reverse said normal position of said contact pairs, and means responsive to a flame at the pilot burner for causing operation of said remain and pilot burners, comprising electrically operable means movable between positions for controlling the supply of fuel to the main burner, relay contacts in series circuit with said movable means and biased to closed position, an electric igniter for the pilot burner in parallel circuit with said movable means, relay contacts in series'circuit with said igniter and biased to open position, operating means for reversing the said positions of said relay contacts and causing energization of said igniter, said operating means being connected in series circuit with said movable means, and means responsive to the flame of the pilot burner for causing said operating means to return said contacts to said biased positions and thereby cause deenergizing of said igniter circuit.

'7. A safety control for fuel burners having main and pilot burners, comprising a control relay, an energizing circuit for said relay including a pair of normally closed contacts controlledby said relay, an electrically operated valve connected in series circuit with said relay and having an open position for admitting fuel to the tacts, thermal resistance means responsive to the flame of the pilot burner, and a second pair of normally open contacts controlled by said relay and adapted to be closed upon said operation of said switch to connect said resistance means in series circuit with said relay and for shunting said valve, said resistance means upon responding to the flame of the pilot burner becoming eflec-' tive to reduce the current to said relay to restore the normal positionsof all of said contact pairs whereby the valve is opened and fuel is admitted to the main burner, said normal positions of all of said contact pairs being retained until absence of a flame at the pilot burner renders said resistance means ineffective, whereupon said valve is closed and said igniter is energized by operation of said relay.

8. In a fuel burner control system, a main burner, a pilot burner, electrically operable means controlling now of fuel to themain burner, an electric igniter for the pilot burner, a thermal resistor responsive to the presence of a flame at the pilot burner, a relay, a plurality of contacts operatively associated with said relay, and a main switch operable in one position thereof to cause operation of said relay to complete two parallel circuits through certain of said relay contacts, one said circuit including said thermal resistor and said relay and the other said circuit including said igniter, said thermal resistor, being adapted to vary in resistance if said pilot burner produces a flame to cause operation of said relay contacts by said relay to discontinue the circuits throughsaid certain contacts and establish through other of said contacts a single circuit including said thermal resistor and said controlling means. e

9. In a fuel burner control system, a main burner, a pilot burner, a source of electric current, electrically operable means controlling flow of-fuel to the main burner, an electric igniter for the pilot burner, a thermal resistor responsive to the presence of a flame at the pilot burner, a relay having a pivoted armature, a plurality of contacts associated with said relay and adapted to be opened and closed by movement of said armature to establish difierent circuits, one said circuit including said thermal resistor and relay in series, another said circuit including said igniter, said controlling means being effectively short-circuited by operation of said relay when the two said circuits are established, and another said circuit including said controlling means and thermal resistor in series, said last mentioned circuit being established upon heating of said thermal resistor by the'flame of the pilot burner to reduce the current to said relay thereby to cause movement of said armature.

10. A safety control for fuel burners having main and pilotburners, comprising electrically operable means movable between open and closed positions for controlling the supply of fuel to the main burner, a control device in circuit with said means and operable for causing movement of said means between said open and said closed position, means responsive to said closing operation of said device for establishing a second circuit including means for igniting the pilot burner, means connected in the first said circuit 8 another closing operation of said device atleast for a period suflicient to permit the escape of unburned fuel remaining from the previous operation.

11. A safety control for fuel burners having main and pilotburners, comprising electrically operable means movable between open and closed positions for controlling the supply of fuel to the main burner, a control device in circuit with said means and operable for causing movement of said means between said open and said closed positions, means responsive to said closing operation of said vice for establishing a second circuit including means for igniting the pilot burner, means responsive to the heat of the flame of the pilot burner for causing said opening operation of said device, said opening operation being adapted to discontinue said second circuit and render said igniting means in operative during normal running conditions in the burner, said heat responsive means being adapted to cool upon extinguishment of said pilot burner whereby said device will undergo another said closingoperation and will render said igniting means operative, electrical heating means in said first circuit and means electrically connected to said second circuit and subject to heat from said heating means during said normal running conditions and having a cooling period longer than that of said heat responsive means for maintaining said igniting means inoperative upon resumption of said closed position by said and responsive to the flame of the pilot burner for causing said opening operation of said device, said opening operation being adapted to discontinue said second circuit and render said igniting means inoperative during normal run-v ning conditions in the burner, and means electrically connected to said second circuit for maintaining said igniting means inoperative upon cally connected to said igniter for delaying re-- movable means at least for a period sufficient to permit the escape of unburned fuel remaining from the previous operation. 12. A safety control for fuel burners having main and pilot burners and means for supplying fuel thereto, comprising an electrically opererable control device movable between positions in response to variations in the current value supplied thereto for controlling the supply of fuel to the main burner, electrically operable means responsive to movement to one position of said control device for i niting the pilot burner, means responsive to a flame at the pilot burner for reducing said current value, thereby causing movement of said control device to another position and terminating operation of said igniting means, and means electrically connected to said igniting means for delaying resumption of said igniter operationwhen said control device is caused to return to said one position by an increase in said current value upon cessation of the pilot burner flame.

13. Asafet control for fuel burners having main and pilot burners and means for supplying fuel thereto, comprising an electrically operable control device movable between positions in response to variations in the current value supplied thereto for controlling the supply of fuel to the main burner, an electric igniter energizable in one position of said control device for igniting the pilot burner, means including a thermal resistor responsive to a flame at the pilot burner for reducing said current value, thereby causing movement of said control device to another position and terminating operation of said igniter, and thermally responsive means electrisumption of said igniter operation when said control device is caused to return to said one position by an increase in said current value upon cessation of the pilot burner flame.

14. A safety control for fuel burners having main and pilot burners, comprising electrically 9 operable means movable between positions for controlling the supply of fuel to the main burner, switching means in circuit with said movable means and operable for causing movement thereof between said positions, electric igniter means responsive to one operation of said switching means for igniting the pilot burner, means including a thermal resistor responsive to the flame of the pilot burner and connected in said circuit for causing another operationof said switching means thereby changing the po sition of said movable means and terminating operation of said igniter, and thermally responsive means connected in said circuit and having a cooling period longer than that of said thermal resistor for delaying resumption of said igniter operation upon a subsequent one said operation of said switching means.

15. A safety control for fuel burners having main and pilot burners and a source of electrical energy, comprising electrically operable means movable between flow permitting and flow preventin ositions for controlling the supply of fuel to the main burner, a relay having a coil and a switch operable thereby for changing the position of said movable means from said flow preventing to said flow permitting position upon a suflicient variation in the energy value supplied to said coil, a thermal resistor exposed to a flame at the pilot burner and adapted for varying in resistance value upon a variation in the thermal condition of said resistor, a circuit including said coil and switch, said resistor and means cooperable therewith for reducing the energy supplied to said coil to a value suflicient only to prevent said switch operation in one thermal condition of said resistor, said switch being operable upon a further reduction in said energy value in another thermal condition of said resistor for establishing a second circuit including said coil and switch, said resistor, and said movable means in said flow permitting position.

16. A safety control for fuel burners having main and pilot burners and a source of electrical energy, comprising electrically operable means movable between flow permitting and flow preventing positions for controlling the supply of fuel to the main burner, a relay having a coil and a switch operable thereby for changing the position of said movable means from said flow preventing to said flow permitting position upon a suiiicient reduction in the energy value supplied to said coil, a thermal resistor exposed to a flame at the pilot burner and adapted for increasing in resistance value upon being heated by said flame, a circuit established by one operation of said switch in the unheated condition of said thermal resistor and'including said coil and switch, said thermal resistor and a fixed resistor cooperable therewith for reducing the energy supplied to said coil to a value sufficient only to prevent said switch operation and to maintain said movable means in said flow preventing position, said movable means being shunted by said switch in said one operation thereof, said switch being operable upon a further reduction in said energy value in the heated condition of said ballast resist-or for establishing a second circuit including said coil and switch, said thermal resistor and said movable means in said flow permitting position, said fixed resistor being rendered inoperative by said switch in said other operation thereof.

17. In a control system for a fuel burner having a source of electrical energy, the combination of a relay having a coil and a switch oper able thereby between positions upon a suflicient variation in the energy value supplied to said coil, a thermal resistor having a preselected teml perature coeflicient of resistance and located to be heated by a flame at the burner for varying in resistance value, said switch being operable upon energization of said coil when said thermal resistor is unheated to a position for establishing a circuit including said coil and switch and said thermal resistor, and a fixed resistor included in said circuit and cooperable with said thermal resistor and said coil for reducing the energy value supplied, to said coil to a value sufficient only to maintain said switch position but insuflicient to establish said position, said switch being operable upon a further reduction in said energy value upon said thermal resistor becoming heated for establishing a second circuit including said coil and switch and said thermal resistor, said fixed resistor being shunted by said switch when said second circuit is established.

CHARLES K. STROBEL. STANLEY J. LAKOTA.

REFERENCES CITED The following references are of record in the 

